I'm guessing it's a diesel,and the developing noise is a leaking pipe between the turbo outlet and the intercooler.This has suddenly split/blown off causing the loss of power.Also,another thing to check is the flexible pipe between the air filter and the turbo inlet.These can go too soft with age and be sucked flat,causing similar power loss to leaks on the pressure side.You won't be able to see this happen,but it does,I have seen it several times when engines have been running at power on a test bed.